1. Field of the Invention
The present invention relates to an image processing apparatus which performs various image processing operations of an input image to edit the image.
2. Related Background Art
In recent years, digital color copying machines are becoming popular. In a copying machine of this type, a color original is color-separated and read in units of pixels, read image data is digitally processed, and obtained digital signals are output to a color printer, thereby obtaining a digital color hard copy. Since an apparatus of this type can digitally process image data, various image processes are available, and an application range in the field of color copy tends to be widened. In the image process modes, an output position of an image is shifted (FIG. 72A), a desired image area is extracted (FIG. 72B), only a color in a desired area is converted (FIG. 72C), a character or image stored in a memory is fitted in a reflective original (FIG. 72D), and so on.
Therefore, upon combination of various functions, a digital color copying machine can be easily applied to color planning reports, advertising posters, sales promotion references, design drawings, and the like.
Requirements for outputting images and characters to be worthy of their names are increasingly demanded for a color reflective original. In order to meet these requirements, character and image portions are separated by image area separation, so that high-resolution processing is performed for the character portion, in particular, processing for printing black characters in only black color is performed, and multigradation processing is performed for the image portion.
However, in the conventional image area separation, a luminance signal Y is used as a dot detection signal, and is given by: EQU Y=0.3R+0.6G+0.11B
Since the luminance signal (Y) has no correlation with chromaticity, it cannot cope with extraction of a color dot signal. As a result, error judgement of a color dot portion occurs.
Therefore, when image area separation is performed by dot judgement to separate a character portion from a dot image portion, and different processing operations are executed for these separated portions, image quality is undesirably degraded due to error judgement.
This also occurs when a color halftone image or a color character is judged. U.S. Pat. No. 4,930,007 discloses a technique in which image area separation is performed in accordance with a minimum value signal of Y (yellow), M (magenta), and C (cyan), i.e., a black signal in UCR.
However, with this arrangement, appropriate image area separation is disturbed when an image having a small Min(Y, M, C) value, e.g., a yellow character, is to be separated.